Disable the build of the nagios-plugin subpackage

The package can not be installed in RHEL, because nagios is missing.
Make it conditional and by default disabled on RHEL to unbreak build
installation.

Resolves: rhbz#2054132

bacula.spec

@@ -1,6 +1,12 @@
 %global uid 133
 %global username bacula
 
+%if 0%{?rhel} && ! 0%{?epel}
+%bcond_with nagios
+%else
+%bcond_without nagios
+%endif
+
 Name:               bacula
 Version:            11.0.1
 Release:            4%{?dist}
@@ -270,6 +276,7 @@ based on a client/server architecture.
 
 This development package contains static libraries and header files.
 
+%if %{with nagios}
 %package -n nagios-plugins-bacula
 Summary:            Nagios Plugin - check_bacula
 Requires:           bacula-libs%{?_isa} = %{version}-%{release}
@@ -277,6 +284,7 @@ Requires:           nagios-common%{?_isa}
 
 %description -n nagios-plugins-bacula
 Provides check_bacula support for Nagios.
+%endif
 
 %prep
 %autosetup -p1
@@ -343,7 +351,9 @@ sed -i 's|^runpath_var=LD_RUN_PATH|runpath_var=DIE_RPATH_DIE|g' libtool
 
 %make_build
 %make_build -C src/tools/cdp-client
+%if %{with nagios}
 %make_build -C examples/nagios/check_bacula
+%endif
 
 pushd src/qt-console/tray-monitor
     %{?qmake_qt5}%{!?qmake_qt5:qmake-qt5} tray-monitor.pro
@@ -354,7 +364,9 @@ popd
 %install
 %make_install
 %make_install -C src/tools/cdp-client
+%if %{with nagios}
 %make_install -C examples/nagios/check_bacula
+%endif
 
 # This will be managed through alternatives, as it requires the name to NOT
 # change between upgrades, so the versioned library name can not be used.
@@ -622,8 +634,10 @@ exit 0
 %{_libdir}/libbacsd.so
 %{_libdir}/libbacsql.so
 
+%if %{with nagios}
 %files -n nagios-plugins-bacula
 %{_libdir}/nagios/plugins/check_bacula
+%endif
 
 %changelog
 * Mon Aug 09 2021 Mohan Boddu <mboddu@redhat.com> - 11.0.1-4